shiva garg1
- Feb 2, 2004
- 49
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I am using electronic workbench.
I built this project for school. Its working very good. I guess people here dont know how to build if its dosent work for them.
Only change I did is instead of U5 leg 4 going to ground, its going to -9v.
Its working very good and i can hear my heart beep very good and high.
Only change I did is instead of U5 leg 4 going to ground, its going to -9v.
Its working very good and i can hear my heart beep very good and high.
Tomah,
Thank you for the confirmation. The project also simulates well in Electronic Workbench as Shiva has told us.
It is normal to see more posts from those who need help on a project than from those who have no problems with a project.
I really appreciate to hear from those who have success. Your feedback is very beneficial to others. It gives others faith that the project is workable.
MP
Thank you for the confirmation. The project also simulates well in Electronic Workbench as Shiva has told us.
It is normal to see more posts from those who need help on a project than from those who have no problems with a project.
I really appreciate to hear from those who have success. Your feedback is very beneficial to others. It gives others faith that the project is workable.
MP
audioguru2
- Apr 6, 2004
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Tomah,
That is wonderful that your project works well. ;D
You are clever to change it so that U5 has a proper negative supply voltage.
Try connecting the junction of C3 and R7 to pin 6 of U2, and change C2 to 4.7uF, with its + terminal towards the microphone. Please let us know the results.
What is the impedance of your earphones? ???
That is wonderful that your project works well. ;D
You are clever to change it so that U5 has a proper negative supply voltage.
Try connecting the junction of C3 and R7 to pin 6 of U2, and change C2 to 4.7uF, with its + terminal towards the microphone. Please let us know the results.
What is the impedance of your earphones? ???
Why would he want to change anything if it is working?
Tomah, I introduce you to audioguru, one who has not built this circuit but has made the statement that the project will not work without his specified changes. I guess he was wrong.
MP
Tomah, I introduce you to audioguru, one who has not built this circuit but has made the statement that the project will not work without his specified changes. I guess he was wrong.
MP
audioguru2
- Apr 6, 2004
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MP,
No, I wasn't wrong:
1) Tomah's project didn't work until he made a change that I discussed above.
2) Shiva's three circuits had no output from U5 without this change, but his computer simulation did not catch this error and therefore worked.
I'll bet that Tomah's earphones' impedance is much more than 8 ohms so that the low-current-output 741 opamp can drive them.
Tomah's slightly modified circuit makes his heart sound like a "beep". I don't think that is a correct heartbeat sound since with another couple of changes then it will produce the correct low-frequency "thump" sound. Why not try a couple more changes to make it much better?
Note that I have not mentioned yet that Tomah's U5 is running "open loop" without any feedback, with AC and DC gain of 100,000 or more. What signal corruption does that cause? Maybe his "beep" is more like a high-frequency "buzz". Should a heartbeat sound like that?
Terribly wrong!!! audioguru.
You posted a long winded page of 8 necessary changes, and you did not even build the circuit. Before you stated that this circuit could not work. Now you state that it does not work well. Others have made the circuit work without the 8 necessary changes. Why is this circuit able to work for others without your corrections? In fact, no one has built it "WITH" your 8 suggestions, so we do not know in fact that your theories work well (they might, but we do not see the working circuit). I will have to go with the proof, not the theory. From the replies, I will have to consider your changes unnecessary.
MP
You posted a long winded page of 8 necessary changes, and you did not even build the circuit. Before you stated that this circuit could not work. Now you state that it does not work well. Others have made the circuit work without the 8 necessary changes. Why is this circuit able to work for others without your corrections? In fact, no one has built it "WITH" your 8 suggestions, so we do not know in fact that your theories work well (they might, but we do not see the working circuit). I will have to go with the proof, not the theory. From the replies, I will have to consider your changes unnecessary.
MP
audioguru2
- Apr 6, 2004
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Only 3 of my changes are important and were also discussed by other members. The other changes only make it better (low-noise microphone preamp, etc).
Has ANYONE made this project work without any changes?
Has ANYONE made this project work without any changes?
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prateeksikka
- Jun 19, 2004
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hi every body, i have spend 3 precious months of my college life working on this project of electronic stethoscope.i made it thrice with one of my friend's help but could not hear anything other than humming noise in the speakers.soldering is perfectly alright.when i tried to trouble shoot it using a c.r.o i got an amplitude modulated kind of waveform at the output . please help.
prateek
prateek
audioguru2
- Apr 6, 2004
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Hi Prateek,
Welcome to our forum.
I am sorry that you are having trouble with this project.
Have you tried any of the corrections that I have recommended in this thread?
Welcome to our forum.
I am sorry that you are having trouble with this project.
Have you tried any of the corrections that I have recommended in this thread?
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audioguru2
- Apr 6, 2004
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Prateek,
Speakers?
Are you using speakers instead of earphones?
Maybe the microphone could hear the speakers and the circuit produced acousical feedback. When low-pass-filtered, it would make a humming noise in the speakers with an amplitude-modulated waveform.
Speakers?
Are you using speakers instead of earphones?
Maybe the microphone could hear the speakers and the circuit produced acousical feedback. When low-pass-filtered, it would make a humming noise in the speakers with an amplitude-modulated waveform.
Hey guys
I have made this circuit but I am using a scope so I do not have a U5 stage yet. I get good audio signals when I look at the output using the elec mic when I speak into it. However when I place it on my skin I cannot pick up the heart beats.
What do u think is the cause of this? I have not used a stethoscope cap or bottle cap, could this be the reason?
Many thks
I have made this circuit but I am using a scope so I do not have a U5 stage yet. I get good audio signals when I look at the output using the elec mic when I speak into it. However when I place it on my skin I cannot pick up the heart beats.
What do u think is the cause of this? I have not used a stethoscope cap or bottle cap, could this be the reason?
Many thks
audioguru2
- Apr 6, 2004
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Hi Damras,
Welcome to our forum.
To pickup a heartbeat sound, the microphone must not touch the skin, but should be spaced a short distance away. A stethoscope head (or jar lid) provides this spacing, surrounds the skin around the listening location and blocks background sounds. It is important to use one.
The original value of C2 is much too small to pickup low-frequency heartbeat sounds. That is why I recommended to replace it with 4.7uF, with its positive terminal toward the microphone.
The original article also has an error in the schematic: the connection of C3 and R7 should also be connected to U2's pin 6.
If you later add U5, then it should be an LM386 (not a 741 as shown), with its pin 6 connected to +9V, its pin 5 connected to R14 and C6 and its pin 7 not connected. It will have a voltage gain of 20 times.
Welcome to our forum.
To pickup a heartbeat sound, the microphone must not touch the skin, but should be spaced a short distance away. A stethoscope head (or jar lid) provides this spacing, surrounds the skin around the listening location and blocks background sounds. It is important to use one.
The original value of C2 is much too small to pickup low-frequency heartbeat sounds. That is why I recommended to replace it with 4.7uF, with its positive terminal toward the microphone.
The original article also has an error in the schematic: the connection of C3 and R7 should also be connected to U2's pin 6.
If you later add U5, then it should be an LM386 (not a 741 as shown), with its pin 6 connected to +9V, its pin 5 connected to R14 and C6 and its pin 7 not connected. It will have a voltage gain of 20 times.
Dear friends,
Sorry for not being present for the discussion. Just like MP said, I've ,made a successful project (a gadget) out of the circuit given in this discussion. It successfully detects 25 different heart diseases and now I'm on my try to commercially implement this. But the problem comes only on the Head design( not in the circuit). But I got some creative suggestions form this forum later and till now I couldn't try it out. I'll sure inform all the outcomes.
Regards
CDAK
Sorry for not being present for the discussion. Just like MP said, I've ,made a successful project (a gadget) out of the circuit given in this discussion. It successfully detects 25 different heart diseases and now I'm on my try to commercially implement this. But the problem comes only on the Head design( not in the circuit). But I got some creative suggestions form this forum later and till now I couldn't try it out. I'll sure inform all the outcomes.
Regards
CDAK
audioguru2
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Damras,
You shouldn't have acoustical feedback between the mic and earphones if you use a stethoscope head (or jar lid) to surround the mic, and use enclosed earphones.
CDAK's mic preamp circuit is posted ealier in this thread. He didn't use earphones but instead used external digital filters feeding a computer monitor.
You shouldn't have acoustical feedback between the mic and earphones if you use a stethoscope head (or jar lid) to surround the mic, and use enclosed earphones.
CDAK's mic preamp circuit is posted ealier in this thread. He didn't use earphones but instead used external digital filters feeding a computer monitor.
[first thank u for the circuit and the forum-----i am a physition and just do circuits as it is---so forgive me for my silly qwustians and my bad languitch as i am egyptian--- i ask about connecting the common earth and the negative volt----- are they connected together??? and if not how can i connect the battery??????thanx alot
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